Oct 10, 2017
Dr. Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. I'm Dr. Carolyn Lam, Associate Editor from the National Heart Center, and Duke-National University of Singapore.
We know that excessive sedentary time is bad in terms of health outcomes, but does it matter how that sedentary time is accrued, whether in short or long bouts? Today's feature paper gives us some answers. More soon, right after the summary of this week's journal.
The first original paper in this week's journal provides insights into the mechanisms underlying neointima formation in arterial restenosis. Co-first authors, Dr. Cheng and Shi, corresponding author Dr. Li from Wuhan University in China, and their colleagues, performed an elegant series of experiments in which they demonstrated that interferon regulatory factor 4, or IRF4, which is a member of a family of key, innate, immune regulators known to play a role in cardiometabolic disease, actually protects arteries against neointima formation.
They further probed the mechanism underlying this protective effect and found that IRF4 promoted the expression of Krüppel-like factor 4 by directly binding to its promoter. Genetic over-expression of Krüppel-like factor 4 in smooth muscle cells reversed the neointima promoting effect of IRF4 ablation. Whereas, ablation of Krüppel-like factor 4 abolished the protective function of IRF4, thus indicating that the protective effects of IRF4 against neointima formation were Krüppel-like factor 4 dependent.
These findings suggest that the previously undiscovered IRF4 Krüppel-like factor 4 axis plays an important role in vascular proliferative pathology and thus may be a promising therapeutic target for the treatment of arterial restenosis.
The next paper highlights that high-spacial resolution in gene expression signatures can reveal new regulators, genetic pathways, and transcription factors that are active in well-defined regions of the heart.
Now we know that traditional genome-wide transcriptome analysis has been disadvantaged by the fact that the signals are derived from tissue homogenates. Thus, the authors of this current paper, including Co-First authors Dr. Lacraz and Junker, corresponding author Dr. Van Rooij from University Medical Center Utrecht in the Netherlands used tomo-seq to obtain genome-wide gene expression signature with a high spacial resolution, spanning from the infarcted area to the remote areas to identify new regulators of cardiac remodeling.
Using this technique, they identified SOX9 as a potent regulator of cardiac fibrosis. In vivo loss of SOX9 reduced the expression of many extracellular matrix genes, which coincided with a blended cardiac fibrotic response upon ischemic injury.
These data therefore were able to unveil currently unknown relevance of SOX9 as a key regulator of cardiac fibrosis, thus underscoring that tomo-seq can be used to increase our mechanistic insights into cardiac remodeling, and to help guide the identification of novel therapeutic candidates.
The next paper reports the primary results of the effect of ferric carboxymaltose on exercise capacity in patients with iron deficiency and chronic heart failure, or EFFECT-HF study, which is a randomized control trial of intravenous ferric carboxymaltose, compared to standard of care on the primary end point of change in peak Vo2 from baseline, to 24 weeks in patients with symptomatic, chronic heart failure with reduced ejection fraction and iron deficiency.
In this report from Dr. van Veldhuisen from University Medical Center Groningen and colleagues, intravenous ferric carboxymaltose was shown to significantly increase serum ferritin and transferrin saturation. At 24 weeks, peak Vo2 had decreased in the control group, but was maintained in the group receiving intravenous ferric carboxymaltose.
Although a favorable effect on peak Vo2 was observed with ferric carboxymaltose, compared to standard of care in the primary analysis, this effect was highly sensitive to the imputation strategy for peak Vo2 among patients who died.
They also reported that patient's global assessment and functional class, as assessed by New York Heart Association, improved on ferric carboxymaltose compared to standard of care.
Whether ferric carboxymaltose is associated with an improved outcome in these high risk patients, deserves further study.
The final study provides important long term clinical data to guide lead management decisions in patients with cardiac implantable electronic devices.
Dr. Pokorney from Duke University Medical Center in Durham, North Carolina, and colleagues, analyzed over 6,000 Medicare patients and found that device extraction was associated with a lower adjusted five year infection rate, compared with a cap and abandon strategy. There was a lower absolute five year mortality with extraction, but after adjustment there was no association between extraction and a lower five year mortality.
In summary, therefore, elective lead extraction for non-infectious indications in this Medicare cohort had similar long term survival, but lower risk of device infections at five years, compared to capping and abandoning leads.
Patient and provider preferences are critical to decision making when considering extraction versus capping and abandonment of leads.
Well, that wraps it up for your summaries. Now for our feature discussion.
For today's feature discussion, we are talking about sedentary time and a metabolic risk of having too much of it. But, today's paper is so interesting because it tells us that it's not just the total amount of sedentary time that may matter, but how we accrue the sedentary time. Very, very novel concept in my point of view and I'm so pleased to have the first and corresponding author of this paper, Dr. Keith Diaz from Columbia University Medical Center with us, as well as Associate Editor from Johns Hopkins, Dr. Wendy Post.
So pleased to have you both. Keith, could we just dive right into it? Tell us what population you were looking at, and what you found.
Dr. Keith Diaz: Sure, so we were studying a population of participants enrolled in the Hispanic Community Health Study, so it's a US populations of over 16,000 Hispanic adults. And essentially what we found was that sitting for prolonged bouts, so sitting for one, two hours at a time, was associated with poor glucose regulation.
Dr. Carolyn Lam: Well, yikes. I've actually been sitting for a few hours in a row right now, actually. I think these results are phenomenal, but could you maybe expand a little bit on the details, like how long is too long? And, how often a break needs to happen for you to see differences in the metabolic risk?
Dr. Keith Diaz: It's a good question and, to be honest, we don't know. I think that's where the research needs to head, but right now it seems to be that taking a break every 30 to 60 minutes could be beneficial. I think that's what we've found thus far.
Dr. Wendy Post: Keith, we were really excited to get your paper in. I think everyone on the Associate Editorial Board was especially interested in it because we can all relate. As Carolyn said, she's been sitting for a long time and when we have these meetings we have two hour meetings at a time and maybe we need to start saying that in the middle we should all stand up and take a break. So we can all relate to this.
But I think one the biggest questions that we had related to data itself, was the association between the total sedentary time and the sedentary bout duration. Maybe you can tell us a little bit more about those correlations in the interaction and tell us also how you also measure sedentary bout duration and total sedentary time in this observational cohort.
Dr. Keith Diaz: Sure, so I'll start with that latter question. So, we measured sedentary time [inaudible 00:09:32] subjectively. So we actually used an activity monitor called an accelerometer to see how sedentary they are. And how we quantified sedentary bouts is we just looked at how long consecutively a person sat without moving. That was considered sedentary bout. In terms of correlation, what we found is that there are very closely linked. So, people who sit for long hours during the day for total volume, also sit in long bouts. And so what we wanted to do was try to figure out and piece apart, which one is more important? When we're trying to ... If we're thinking about guidelines and what we should be doing about our sedentary time, is it important to reduce our volume or interrupt our bouts? And so what we found is that they're not independent, and that they're in many ways synergistic. And that the association of prolonged sedentary bouts with glycemic biomarkers varied according to how much total volume you sit and vice-versa.
Dr. Wendy Post: Can you expand a little bit more on that? So tell us about the interaction that you found between sedentary bout duration and total sedentary time.
Dr. Keith Diaz: Sure, so we did find that there was a specifically significant interaction between the two variables and so what we tried to do is actually categorize people as to whether they were high for both characteristics or high for just one of them. And so what we found was that those participants who are high for both, so they had high volume and sat in long bouts, they had the worst glucose regulation, and that those individuals that were high for just one of the characteristics had a little bit better glucose regulation. And so really what we thought the take home message was when thinking about how do we improve our sedentary behaviors is that it's targeting both. It's not sitting for large volumes during the day, but also making sure to take frequent breaks every 30 or 60 minutes.
Dr. Wendy Post: And tell us about the glucose measures that you included in your study.
Dr. Keith Diaz: Yep, we had a couple glucose measures. One we had people do a two hour glucose tolerance test, so they took a glucose drink and then we measured their blood sugar levels two hours after having that drink. We also measured their H1Ac levels as well as their fasting glucose and fast to link insulin measures from which we can then derive measures of something called HOMA IR, which is a measure of insulin resistance.
Dr. Wendy Post: And the associations that you saw were primarily with the HOMO IR and the two hour glucose levels but less with the hemoglobin A1c?
Dr. Keith Diaz: Correct.
Dr. Wendy Post: So it really appears to be that insulin resistance that's most affected by the total sedentary time and sedentary bout duration. Tell us about potential confounders and how you factored that into your analysis.
Dr. Keith Diaz: Yeah, there was quite a number of potential confounders between this relationship of sedentary behavior and glycemic biomarkers. One of them in particular that we were concerned about most were things like body mass index or exercise or physical activity levels. And so we took a look at what we adjusted for those confounders how the relationship changed. And what we did find was that there was an attenuation and association between sedentary behavior and the glucose markers, but there was also ... were still statistically significant. So suggestive that maybe they're partly in the pathway of body mass index or exercise but they didn't make the relationship go away. I should add that we looked at a couple other confounders, we looked at things like inflammation, C-reactive protein, as well as whole bunch of other measures of cardiovascular risk factors. I'll stop there.
Dr. Wendy Post: And what about the fact that study is cross-sectional, are there any caveats related to the study design that you'd like to point out to the audience?
Dr. Keith Diaz: Yeah, I think that's an important point, that this is cross-sectional, so by no means can we infer causality that sedentary behavior causes glucose dysregulation, it's just purely an association. So I think anyone listening to this podcast should keep that in mind when reading this paper or listening to this podcast.
Dr. Wendy Post: So if you were writing the next set of guidelines what would you recommend in terms of how you implement these findings into guidelines? Not to imply that we think that these cross-sectional observational data mean that we're ready to change guidelines but, if these were replicated in randomized trial or some other more objective data study design, how do you think we should use these results to change our behaviors?
Dr. Keith Diaz: I think these guidelines point ... or, with the current guidelines are, sit less, move more, where the guidelines that came out from AHA in October of 2016. In part, they were not as specific because we don't have quite the quality of guidelines or data that we need for more qualitative guidelines, or quantitative guidelines. I think if we're able to replicate these data with [inaudible 00:14:10] or point us towards at least is, also, that we should be interrupting our sedentary bouts. And so what I'd like to see hopefully if we can replicate something I'd like guidelines that say every 30 minutes or every 60 minutes of sitting you should stand up and move. And hopefully with future studies that are coming out that we can make them even more specific and something along the lines of every 30, 60 minutes you stand up and walk for 5 minutes or you just stand up for 1 minute. That's where I'd like to see the science head and I think this study points us in the that direction of maybe we have to start thinking about breaking up our sedentary bouts.
Dr. Carolyn Lam: All right you guys, I don't know about you, but I am literally standing up right now while I'm listening to you both. This is so interesting and I love the way, Wendy, you reflected the robust discussions we had as team when we were working through this paper. Congratulations again, Keith, for just this remarkable paper. Actually, maybe I could just ask, Wendy, what do you think? What do you think our next steps that may need to get these kinds of recommendations, perhaps into guidelines?
Dr. Wendy Post: I think as was alluded to before, these are observational data so they're important for hypothesis generation, but really to have evidence that would lead to changes in guidelines maybe having a randomized trial, where obviously you can't have very hard outcomes, but randomized trials of some duration that could potentially lead to changes and important outcomes, would then maybe lead to changes in guidelines. But there isn't anything that we would lose from trying to implement these kinds of behavior, changes into our lifestyle since the downside and the risk is pretty low. So even if they don't make the strongest level of evidence at this point, I think we can still all be mindful of this and so.
One thing that we've been trying to do in our preventive cardiology group at Hopkins is trying to implement walking meetings. In fact, I just had an email discussion with one of my colleagues about meeting tomorrow and she said, "Well, where do you want to meet?" And I said, "Well, why don't we go for a walk? The weather should be nice." And so I think if we're all mindful of trying to, not only increase our amount of physical activity, but trying to limit the sedentary bout duration by being creative and trying to change, sort of, long standing traditions of having meetings sitting in an office, then that could be helpful.
So, just something for our audience to think about as well.
Dr. Carolyn Lam: That's brilliant. You know, the one thing that I was thinking, though, just thinking about the reception of these data in my country, in where I practice, in Asia. This was a purely Hispanic or Latino population. I suppose there is a perception that that population may be predisposed to cardiometabolic disease and so on, and so you know, what's the applicability to us in Asia? So, I'm really happy, particularly to hear how you've taken it on. I mean, it's a simple thing, why not, right? Just to be more active. There's surely can't be something wrong with that. What do you think of that?
Dr. Wendy Post: Totally, I think it's important to emphasize the unique nature of these data and that they come from a Hispanic study, which is a really important addition to our literature in epidemiology and cardiovascular disease and certainly there are significant differences in lifestyle among different communities within the United States and across the globe, as you've experienced having lived in different countries. And so, I think we need obtain more data about how there might be differences based on various traditions and different lifestyles, and try to target those who are at greatest risk.
Dr. Carolyn Lam: Keith, did you have anything to add to that?
Dr. Keith Diaz: Yeah, I think Wendy is right on and certainly I don't think we have any reason to suspect that sedentary behavior acting differently in Hispanics versus other populations, and so I still think going forth with this notion that we all should be reducing our sedentary behaviors is important to highlight.
Dr. Carolyn Lam: Fantastic. Well, thank you both for a really wonderful discussion. This is really cool, I think a lot of people will be talking about this.
Listeners, you've heard it first, though, in Circulation on the Run. Thank you for joining us today and don't forget to tune in next week.